1. Field of the Invention
The present invention refers to a device for measuring an electrical parameter in the milk during the milking of an animal, comprising a transportation member, arranged to transport the milk from a teat of said animal to a milk collecting member of a milking machine and forming a passage for the milk to be transported, and at least two electrodes provided to be in contact with the milk flowing through the passage and connected to an evaluation unit.
2. Description of the Prior Art
It is known that the electrical conductivity of the milk is changed when the milk is infected because of mastitis or milk fever, for instance. In particular, the number of ions increases in these cases, resulting in an increase of the conductivity of the milk . By measuring the conductivity of the milk, it is thus possible to determine whether the milk is infected. An acute inflammation of an udder gives a relatively great change of the conductivity of the milk and is thus relatively easily detected by means of such a measurement. Theoretically, it is however a precondition that such a measurement of the conductivity is performed on a known volume and in practice this means that in order to obtain comparable conductivity values a certain quantity of milk has to be located between the measurement electrodes. If this quantity is not determined in a secure manner or is not equal at each milking occasion, merely a value of the conductance of the actual unknown milk quantity is obtained. In particular, in connection with latent inflammations of the udder, it is important that the measurement is performed on a certain quantity of milk since such a latent inflammation merely results in a small change of the conductivity of the milk.
EP-A-397 274 discloses a mastitis detector having electrodes for measuring the conductivity of the milk from a teat. The detector is provided in a milk conduit and comprises a cup shaped chamber which is open upwardly against the direction of the milk flow. The electrodes are provided in the bottom surface of the chamber. When the milk is flowing through the milk conduit a quantity thereof will be collected in the chamber and be in contact with the electrodes. Thereby, a measurement of the conductivity of the milk may be performed. However, the detector disclosed does not guarantee a flow through the chamber but at least a part of the collected milk quantity present in the chamber remains therein irrespective of how much milk is flowing through the milk conduit. This means that also when the milk flow has ceased the detector will provide a conductivity value for the milk which still may be present in the chamber.
GB-A-2 124 877 discloses a device for indicating a milk flow through a milk conduit of a milking machine. The milk conduit is provided between a claw and a collecting member of the milking machine. The milk conduit comprises two electrodes provided one after the other in the direction of the milk flow and each consisting of an open cylinder abutting the inner wall of the milk conduit. A voltage is applied to the electrodes and thus the variations in the conductance of the milk flowing through the milk conduit is measured. The result of these measurements are utilized for interrupting the milking when the mean value of said measurements falls below a certain value. However, by means of the device disclosed it is not possible to know how much milk there is between the two electrodes and therefore no reliable value of the conductivity of the milk may be obtained.
EP-B-137 367 discloses a milking device comprising measurement equipment for detecting the milk flow from an individual teat. The value detected may be utilized for determining when the milking from this teat is to be interrupted. The measurement equipment comprises two electrodes for each milk flow to be detected. According to a first embodiment, a milk conduit for a milk flow comprises a main passage and a secondary passage in which two electrodes are provided. At the end of the secondary passage there is a small hole permitting the milk to flow from the secondary passage back into the main passage. In such a manner a flow through the secondary passage is obtained. However, the small hole is very sensitive for dirt particles or fat agglomerations, which may be present in the milk and which tend to stop up the small hole. In such a manner the flow through the secondary passage is interrupted and no proper conductivity value for the milk is obtained. According to another very simple embodiment, the milk conduit comprises a throttling, and upstream of the throttling two electrodes. By this simple device it is merely possible to determine whether milk has been collected in the area above the throttling. It is to be noted that the throttling of course has to be provided in such a manner that it permits a relatively large milk flow therethrough. According to a third embodiment, the milk is conducted from each teatcup to a claw having a main passage. In addition, for each teatcup a secondary passage is provided in the claw in such a manner that a certain quantity of the milk from a teatcup will be conducted into a respective secondary passage. The secondary passage comprises two electrodes for measuring the conductivity of the milk being present in the secondary passage. In the same way as in the first embodiment, there is a small hole at the end of the secondary passage connecting the secondary passage to the main passage. In such a manner, a flow through the secondary passage is ensured. Also in this case the risk of stopping up the hole is significant.
U.S. Pat. No. 4,325,028 discloses a device for measuring the conductivity of the milk from each individual teat in a milk conduit between the teatcup and the claw. The measurement equipment comprises a receiving device, provided in each such milk conduit and having electrodes located therein, and an electronic evaluation device. The construction of the receiving devices are not described more closely. The aim of the device disclosed is to enable the determination whether the conductivity value of the milk from an individual teat is abnormal and thus whether any udder part is inflamed.
WO 83/03305 discloses an electrical conductivity device for detecting mastitis in the milk from a cow by measuring the conductivity of the milk. The device is intended in the first place for manual use although it is mentioned that it may be provided near a claw of a milking machine. The device is adapted to collect a minor secondary milk flow of the main milk flow and conduct this secondary milk flow through a testing passage in the form of a flexible tubing comprising two electrodes. The flexible tubing is relatively thin and there is a risk that dirt particles or fat agglomerations may stop up the milk flow therethrough.
WO 95/22888 discloses a claw for a milking machine having means for measuring the complex impedance, such as the electrical conductance and/or the capacitance, of the milk in order to detect mastitis. The claw comprises four inlet members and four chambers provided beneath a respective inlet member for collecting a part of the milk flowing through the inlet member into the claw. In the bottom wall of the chamber there is a small opening permitting the milk collected therein to slowly drain away. Also this known device provides a risk that dirt particles and fat agglomerations stop up the milk flow through the small opening.
The object of the present invention is to remedy the problems mentioned above and provide an improved device for measuring an electrical parameter of the milk. In particular, the invention aims at a device permitting the measurement of small milk flows and simultaneously ensuring a continuous milk flow through the measurement location.
This object is obtained by the device initially defined and characterized in that the transportation member comprises a wall member provided in the passage and forming a groove being open towards the passage, said electrodes being provided on the wall member in the groove, and that the wall member is provided to receive a part of the milk flowing through the passage, said groove being shaped in such a manner that at least a part of said received part of the milk flows through the groove while contacting said electrodes. By such a construction at least a part of the quantity of milk received by the wall member may be distributed in a continuous flow through the groove in such a manner that the latter always will be essentially filled with milk and thus the quantity of milk present between the electrodes is essentially determined. When the grooves are filled with milk it is thus possible to obtain a maximum value of a current flowing between the electrodes. This maximum value may be utilized for determining a comparable value of an electrical parameter, such as the conductance, the impedance, conductivity or resistivity, of the milk. The measurement device according to the invention may thus be utilized for detecting very small changes of the conductivity of the milk. Thereby, a possible state of illness of the animal may be detected at an early stage. By configuring the dimension of the groove in a proper manner, it will also, in the case of relatively small milk flows, be filled with milk and in such a way it is possible also in these cases to obtain such a maximum value. If the conductivity value obtained does not reach the maximum value there is an indication that the milk flow is very small and that the milking process may be interrupted. By comparing the maximum values obtained for the conductivity at different milking occasions one may determine whether the animal is suffering from any decease, for instance mastitis. By such an open groove, the risk of dirt, fat agglomerations or particles of any kind getting clogged in the groove, thereby obstructing the flow through the groove, is substantially reduced. Such a groove is also advantageous from a cleaning point of view as such an open groove is accessible for the injection of cleaning liquid, for instance. Preferably, the groove is shaped in such a manner, with regard to its width and inclination when the transportation member is in an operating position, that the milk flow through the groove is essentially secured. It means that in the case of a small milk flow from the actual teat, a relatively large part of the milk will flow through the groove, in an extreme case essentially all milk, and at a large milk flow a relatively small part of the milk will flow through the groove. In such a manner the measurement will always be performed with respect to the actual milk flow, i.e. the measurement may not be deteriorated by milk remaining in the groove. This also means that by the measurement device according to the invention it is possible to determine in a very reliable manner whether an individual teat produces any milk since if that is the case no milk will remain in the groove.
According to an embodiment of the invention, the wall member comprises a concave surface arranged to collect said part of the milk, the groove extending through said concave surface. Such a concavely shaped wall member will be able to keep said part of the milk and during a certain period of time continuously discharge said part through the groove.
According to an advantageous application of the invention, the transportation member comprises a claw through which the passage extends and in which the wall member is provided. Thereby, the claw may comprise an inlet arranged to permit the supply of the milk to the claw from said teat and the wall member may be provided beneath the inlet when the claw is in an operating position. Furthermore, the concave surface of the wall member faces the inlet. Consequently, the space being present in a claw may advantageously be utilized for the measurement equipment according to the invention. It is to be noted, in particular, that such a claw permits an individual measurement of the electrical parameter of the milk from each of the teats of the animal.
According to a further embodiment of the invention, the groove extends essentially in the flow direction of the milk flowing through the passage. Such a shape also facilitates a continuous flow of milk through the groove. The groove will have no retarding influence on the milk flow through the passage.
According to a further embodiment of the invention, the electrical parameter comprises the conductivity of the milk. Thereby, the groove may have such a depth that a distinguishable maximum value is obtained during the measurement of the conductivity of the milk.
According to a further embodiment of the invention, the groove comprises a longitudinal bottom surface and two longitudinal side surfaces. Preferably, the width of the groove, i.e. the distance between the longitudinal side surfaces, is about 1-6 mm, preferably 2-5 mm. Furthermore, the groove may in the area of the electrodes have a height of about 5-20 mm, preferably 10-15 mm. Preferably, the electrodes are provided essentially opposite to each other on a respective side surface. Furthermore, they may be provided about 0-10 mm, preferably 0-5 mm, above the bottom surface.
According to a further embodiment of the invention, the device comprises four electrodes provided in the groove. Thereby, two of the electrodes may be provided essentially opposite to each other on a respective side surface and two of the electrodes may be provided on the bottom surface. Furthermore, the evaluation unit may be arranged to perform a four-pole measurement by means of the electrodes in such a manner that a voltage is provided between the electrodes provided on the side surfaces, and that the current, required for providing a voltage drop of a predetermined level between the two electrodes provided on the bottom surface, is measured.